Mid-Atlantic Ridge
]] ]] , a visible surface feature of the Mid-Atlantic Ridge, the Easternmost edge of the North American plate. It is a popular destination for tourists in Iceland.]] The Mid-Atlantic Ridge is where seafloor spreading takes place in the middle of the Atlantic Ocean. It is part of a world-wide system of mid-ocean ridges. These ridges make up the longest mountain range in the world, all underwater except for short stretches like Iceland. On Iceland, the Mid-Atlantic Ridge reaches the surface. The ridge separates oceanic tectonic plates, and moves the plates apart at about 2.5 cm per year. The Mid-Atlantic Ridge includes a deep rift valley which runs along the middle of the ridge along almost its entire length. At the rift, the boundary between tectonic plates, magma from the mantle reaches the seafloor. New magma emerges onto the ocean floor near the ridge axis. The crystallized magma forms new crust of basalt and gabbro. History The ridge was discovered during the expedition of HMS Challenger in 1872.Hsü, Kenneth J. 1992. Challenger at Sea. Princeton University Press. p57 A team of scientists on board discovered a large rise in the middle of the Atlantic. They were planning the future location for a transatlantic telegraph cable.Redfern R. 2001. Origins, the evolution of continents, oceans and life, University of Oklahoma Press. p26 The existence of such a ridge was confirmed by sonar in 1925Alexander Hellemans and Brian Bunch 1989. Timeline of science. Sidgwick and Jackson, London. In the 1950s, mapping of the Earth’s ocean floors showed the Mid-Atlantic Ridge to have valleys and ridges.Ewing, W.M; Dorman H.J; Ericson J.N. & Heezen B.C. 1953. Exploration of the northwest Atlantic mid-ocean canyon, Bulletin of the Geological Society of America 64, p865-868 Its central valley is seismologically active and the epicentre of many earthquakes.Heezen B.C. & Tharp, M. 1954. Physiographic diagram of the western North Atlantic, Bulletin of the Geological Society of America 65, p1261Hill M.N. & Laughton A.S. 1954. Seismic observations in the eastern Atlantic, 1952. Proceedings of the Royal Society, series A, mathematical & physical sciences 222, p348-356 Ewing and Heezen discovered the ridge to be part of a 40,000-km-long essentially continuous system of mid-ocean ridges on the floors of all the Earth’s oceans.Edgar W. Spencer 1977. Introduction to the structure of the Earth. 2nd ed, McGraw-Hill, Tokyo. The discovery of this worldwide ridge system led to the theory of seafloor spreading and general acceptance of Wegener's theory of continental drift and expansion as plate tectonics. Geology The ridge started forming in at the end of the Triassic period, and was responsible for the separation of the Americas from Africa and Europe with the breakup of Pangaea. The ridge sits atop a geologic feature known as the Mid-Atlantic Rise which is a progressive bulge that runs the length of the Atlantic Ocean, with the ridge resting on the highest point of this linear bulge. This bulge is thought to be caused by upward convective forces in the asthenosphere pushing up the oceanic crust and lithosphere. References Category:Atlantic Ocean Category:Plate tectonics Category:Geography of Iceland